US6609027B2 - His Bundle sensing device and associated method - Google Patents

Abstract

A cardiac stimulation device, a His Bundle lead, and an associated method for detecting a conduction signal from the His Bundle. Upon this detection, the stimulation device delivers ventricular stimulation to the right and/or left ventricles at an interval following the atrial depolarization. A sensing window is initiated following the sensing of the atrial depolarization. During the sensing windows, the His Bundle signal received through the His Bundle lead is sampled and a moving average is calculated to determine a signal peak. Detection of the His Bundle signal peak triggers ventricular stimulation, which may be delivered to the right ventricle, the left ventricle, or both ventricles.

Description

FIELD OF THE INVENTION

This invention relates generally to implantable cardiac stimulating devices. More specifically, the present invention is directed to a dual-chamber cardiac stimulation device using a lead designed for locating the His Bundle, for fixation to the site of the His Bundle, and for sensing a His Bundle signal. This invention further relates to a method for delivering ventricular stimulation at an optimal atrioventricular delay in patients with bundle branch conduction abnormalities.

BACKGROUND OF THE INVENTION

In a normal human heart, the sinus node, generally located near the junction of the superior vena cava and the right atrium, constitutes the primary natural pacemaker initiating rhythmic electrical excitation of the heart chambers. The cardiac impulse arising from the sinus node is transmitted to the two atrial chambers, causing a depolarization known as a P-wave and the resulting atrial chamber contractions. The excitation pulse is further transmitted to and through the ventricles via the atrioventricular (AV) node and a ventricular conduction system comprised of the bundle of His, the left and right bundle branches, and the Purkinje fibers causing a depolarization known as an R-wave and the resulting ventricular chamber contractions.

Disruption of this natural pacemaking and conduction system as a result of aging or disease can be successfully treated by artificial cardiac pacing using implantable cardiac stimulation devices, including pacemakers and implantable defibrillators, which deliver rhythmic electrical pulses or other anti-arrhythmia therapies to the heart, via electrodes implanted in contact with the heart tissue, at a desired energy and rate. One or more heart chambers may be electrically stimulated depending on the location and severity of the conduction disorder.

A single-chamber pacemaker delivers pacing pulses to one chamber of the heart, either one atrium or one ventricle. Dual chamber pacemakers are now commonly available and can provide stimulation in both an atrial chamber and a ventricular chamber, typically the right atrium and the right ventricle. Both unipolar or bipolar dual chamber pacemakers exist in which a unipolar or bipolar lead extends from an atrial channel of the dual chamber device to the desired atrium (e.g. the right atrium), and a separate unipolar or bipolar lead extends from a ventricular channel to the corresponding ventricle (e.g. the right ventricle). In dual chamber, demand-type pacemakers, commonly referred to as DDD pacemakers, each atrial and ventricular channel includes a sense amplifier to detect cardiac activity in the respective chamber and an output circuit for delivering stimulation pulses to the respective chamber.

If an intrinsic atrial depolarization signal (e.g. a P-wave) is not detected by the atrial channel, a stimulating pulse will be delivered to depolarize the atrium to cause atrial contraction. Following either a detected P-wave or an atrial pacing pulse, the ventricular channel attempts to detect a depolarization signal in the ventricle, known as an R-wave. If no R-wave is detected within a defined atrial-ventricular interval (AV interval, also referred to as AV delay), a stimulation pulse is delivered to the ventricle to cause ventricular contraction. In this way, rhythmic dual chamber pacing is achieved by coordinating the delivery of ventricular output in response to a sensed or paced atrial event.

It is known that the AV delay setting during dual chamber pacing can have profound effects on hemodynamic function, particularly in patients suffering from congestive heart failure. Extreme differences in cardiac output can result from different AV delay settings. The optimal setting varies between individuals and can range from 50 ms to 200 ms. Determining the optimal setting is often difficult since a number of physiological factors influence the hemodynamic function, and hemodynamic measurements required to determine the optimal setting can be costly, time-consuming, and are often invasive with additional inherent risks.

One approach to optimizing the AV delay involves incorporating in the pacemaker system implantable physiological sensors that are capable of detecting a signal that is indicative of the hemodynamic function of the heart. The AV delay can then be adjusted so that the physiological signal measured indicates maximized hemodynamic function. This approach however requires one or more additional sensors, added hardware circuitry, and additional processing time in order to determine the optimal AV delay. Furthermore, the physiological response to a change in AV delay may not be instantaneous but more likely occurs over an extended period of time. Thus, determining the optimal setting may require testing several settings after extended periods of time during which the patient is not receiving optimal stimulation therapy.

In the majority of individuals, the most effective heartbeat is triggered by the patient's own spontaneous pacemaker. The electronic stimulation device is intended to fill in when the patient's spontaneous pacemaker fails or when the heart's conduction system fails. In a large number of heart failure patients, natural conduction through the atrioventricular node and the bundle of His are intact. Disruption of ventricular rhythm in these patients is the result of conduction disorders residing in the left and/or right bundle branches.

Dilatation of the heart due to congestive heart failure (CHF) has been associated with delayed conduction through the ventricles. This delayed conduction exacerbates the hemodynamic inefficiency of the failing heart because of the resulting poor synchronization of the heart chambers.

Direct stimulation of the His Bundle has been found to provide hemodynamic improvement in patients suffering from dilated cardiomyopathy but having normal ventricular activation. Reference is made to Deshmukh P. et al., “Permanent, Direct His-Bundle Pacing—A New Approach to Cardiac Pacing in Patients With Normal His-Pukinjie Activation,” Circulation, 2000;101(8)869-77, Feb. 29, 2000. This result supports the hypothesis that the natural conduction system, when intact, can provide hemodynamically optimal depolarization timing of the heart chambers.

What is needed, therefore, is a cardiac stimulation device capable of delivering ventricular stimulation according to the optimal timing dictated by the heart's own conduction system. It would be desirable, in an implantable dual chamber or multi-chamber cardiac stimulation device, to detect the conduction signal that is naturally conducted through the atrioventricular node and into the His Bundle and trigger ventricular stimulation delivery based on this detected conduction signal.

SUMMARY OF THE INVENTION

The present invention addresses this need by providing a cardiac stimulation device and leads, with an associated method for detecting a conduction signal from the His Bundle, and upon this detection, delivering ventricular stimulation to the right and/or left ventricles. According to one embodiment, the system and method of the present invention advantageously deliver ventricular stimulation at an interval following atrial depolarization that is optimally triggered by the functioning portion of the natural conduction system of the heart, and bypasses the dysfunctional portion of the ventricular conduction system to re-establish rhythmic ventricular contractions with the benefit of efficient hemodynamic output.

A preferred embodiment of the present invention provides an implantable cardiac stimulation device equipped with cardiac data acquisition capabilities. The stimulation device includes a control system for controlling the operation of the device; a set of leads with appropriately positioned electrodes for receiving cardiac signals and for delivering atrial and ventricular stimulation pulses; a set of sensing circuits comprised of sense amplifiers for sensing and amplifying the cardiac signals including a modern low noise amplifier used to sense (and optionally to stimulate the His Bundle) and amplify the conduction signal arising from the His Bundle; a sampler, such as an A/D converter for sampling cardiac signals; an averager capable of determining a moving average of a sampled signal; pulse generators for generating atrial and ventricular stimulation pulses; and an impedance measuring circuit for performing a variety of impedance measurements including a tissue impedance measurement used in locating the His Bundle.

In addition, the stimulation device includes a memory for storing operational parameters for the control system, such as cardiac signal sampling parameters and cardiac signal samples. The device also includes a telemetry circuit for communicating with an external programmer. In the preferred embodiment, the stimulation device further includes a physiological sensor of metabolic demand, such as an activity sensor or a minute volume sensor, that provides feedback to the control system which in turn controls the stimulation rate such that the measured metabolic need is met.

The present invention also provides a His Bundle lead. The His Bundle lead includes a tip electrode at the distal end of the lead for sensing His Bundle conduction signals. The tip electrode is provided with an active fixation device for securing the tip electrode to the His Bundle tissue. The tip electrode also includes a non-traumatic conductive surface used to map the location of the His Bundle prior to fixing the tip electrode in the endocardial tissue. It would also elute an acute anti-arrhythmia drug such as lidocaine and/or an anti-inflammatory agent, to reduce the early PVCs that can be caused by the trauma of the lead implantation.

In an exemplary preferred embodiment, the non-traumatic conductive surface is provided as a mapping collar that functions as a source electrode in performing a tissue impedance measurement for locating the His Bundle during the implantation procedure of the stimulation device and His Bundle lead. The His Bundle lead may further include a ring electrode located between approximately 2 mm and 30 mm, but preferably 10 mm, from the tip electrode to be used in bipolar sensing.

During the implantation procedure, the His Bundle lead is advanced into the right atrial chamber and, when the His electrode is positioned proximate the His Bundle tissue, as indicated by an impedance measurement approximately equal to an expected His Bundle tissue impedance, the active fixation electrode is secured in the His Bundle tissue.

When operating according to a preferred embodiment, the stimulation device control system detects an atrial event, either a sensed atrial P-wave or an atrial stimulation pulse, and initiates a His Bundle signal sensing window beginning almost immediately after the atrial event and extending a predefined amount of time, typically 200 ms.

During the sensing window, the His Bundle signal received through the His Bundle lead is sampled and a moving average is calculated to determine a signal peak. Detection of a His Bundle signal peak triggers ventricular stimulation. Ventricular stimulation may be delivered to the right ventricle, the left ventricle, or both ventricles.

The present invention is particularly advantageous for patients with congestive heart failure (CHF) and having normal conduction paths through the AV node and His Bundle but delayed conduction through the bundle branches or the Purkinje system. Such patients tend to benefit from stimulating the left ventricle (via a lead positioned through the coronary sinus with its electrode(s) in a coronary vein overlying the left ventricle) and the right ventricle almost simultaneously. By sensing the His Bundle signal, the stimulation device can deliver biventricular stimulation with optimal AV delays. The delay from the detected His (or His Bundle) signal to the right ventricular stimulation and the delay from the detected His signal to the left ventricular stimulation may be the same or may be programmable values selected by the clinician in order to achieve a desired synchronization between the left and right ventricular contractions.

In an alternative embodiment, if no His signal is detected, ventricular stimulation may be delivered directly to the His Bundle using the His Bundle lead. This alternative embodiment is beneficial to patients having intact conduction below the level of the His Bundle and having intermittent or partial atrioventricular block. When the atrial depolarization is not conducted through the atrioventricular node, the His Bundle lead may be used to deliver stimulation to depolarize the His Bundle. A depolarization of the His Bundle will then be conducted through the ventricles via the left and right bundle branches and the Purkinje fibers to cause ventricular contraction.

The system and method of the present invention thus provide ventricular stimulation optimally timed following an atrial event according to the heart's natural conduction timing. This optimized ventricular stimulation is accomplished without requiring lengthy testing procedures to determine an optimal AV delay and does not require complex physiological sensors, hardware, or processing algorithms. Patients suffering from congestive heart failure with intact atrioventricular nodal conduction will benefit from improved synchrony of ventricular contractions according to the heart's natural conduction timing. Patients suffering from intermittent atrioventricular nodal block may benefit from His Bundle stimulation with the stimulation device, by providing a bypass of the block and delivering the ventricular stimulation via the remaining intact conduction pathways.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features of the present invention and the manner of attaining them will be described in greater detail with reference to the following description, claims, and drawings, wherein reference numerals are reused, where appropriate, to indicate a correspondence between the referenced items, and wherein:

FIG. 1 is a simplified, partly cutaway view illustrating an implantable stimulation device in electrical communication with at least four leads, including a His Bundle lead, implanted into a patient's heart for delivering multi-chamber stimulation and shock therapy;

FIG. 2 is a simplified, partly cutaway view illustrating an alternative design of an implantable stimulation device, shown implanted into the right chambers of the patient's heart for delivering dual-chamber stimulation and shock therapy;

FIG. 3 is a functional block diagram of the multi-chamber implantable stimulation device of FIG. 1, illustrating the basic elements that provide pacing stimulation, cardioversion, and defibrillation in four chambers of the heart;

FIG. 4 is a partly fragmentary illustration of the distal end of the His Bundle lead for use with the stimulation device of FIG. 3, depicting a tip electrode with an active fixation device and a non-traumatic conductive surface, and a ring electrode;

FIG. 5 is a partly fragmentary illustration of the distal end of another His Bundle lead for use with the stimulation device of FIG. 3, depicting a tip electrode with an active fixation device and a non-traumatic conductive surface, a ring electrode, and a four conductive sensing electrodes;

FIG. 6 is an equivalent circuit diagram illustrating a tissue impedance measurement method using the lead of FIG.4 and the stimulation device of FIG. 3 for locating the His Bundle;

FIG. 7 is a flow chart providing an overview of the methods implemented by the stimulation device of FIG. 3, for providing ventricular stimulation at an optimal time after an atrial P-wave based on the detection of a His signal peak using the lead depicted in FIG. 4;

FIG. 8 is a flow chart providing an overview of the operations included in an alternative embodiment of the present invention for providing ventricular stimulation at an optimal time after an atrial P-wave based on the detection of a His signal median using the lead depicted in FIG.4 and the stimulation device of FIG. 3; and

FIG. 9 is a timing diagram depicting a sequence of events that occur during the operations of FIG.8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated for practicing the invention. This description is not to be taken in a limiting sense but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be ascertained with reference to the issued claims. In the description of the invention that follows, like numerals or reference designators will be used to refer to like parts or elements throughout.

The present invention is directed at providing a method and apparatus for delivering ventricular stimulation at an optimal time delay following atrial depolarization based upon detecting a conducted signal in the His Bundle. One embodiment of the present invention may be implemented in either a dual chamber or multi-chamber cardiac stimulation device. In a preferred embodiment, the present invention is implemented in a rate-responsive multi-chamber cardiac stimulation device such as thestimulation device10 depicted in FIG.1.

With reference to FIG. 1, thestimulation device10 is shown in electrical communication with a patient'sheart12 by way of four leads,20,21,24, and30 and suitable for delivering multi-chamber stimulation and shock therapy. To sense atrial cardiac signals and to provide right atrial chamber stimulation therapy, thestimulation device10 is coupled to an implantable rightatrial lead20 having at least an atrial tip electrode22, which typically is implanted in the patient's right atrial appendage or atrial septum.

To sense left atrial and ventricular cardiac signals and to provide left chamber pacing therapy, thestimulation device10 is coupled to a “coronary sinus”lead24 designed for placement in the “coronary sinus region” via the coronary sinus ostium for positioning a distal electrode within the coronary veins overlying the left ventricle and/or additional electrode(s) adjacent to the left atrium. As used herein, the phrase “coronary sinus region” refers to the vasculature of the left ventricle, including any portion of the coronary sinus, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the coronary sinus which overlies the left ventricle.

Accordingly, an exemplarycoronary sinus lead24 is designed to receive atrial and ventricular cardiac signals and to deliver left ventricular pacing therapy using at least a leftventricular tip electrode26, left atrial pacing therapy using at least a leftatrial ring electrode27, and shocking therapy using at least a leftatrial coil electrode28. In another embodiment, an additional electrode for providing left ventricular defibrillation shocking therapy may be included in the portion of the lead overlying the left ventricle, adjacent to thering electrode25.

Thestimulation device10 is also shown in electrical communication with the patient'sheart12 by way of an implantableright ventricular lead30 having, in this embodiment, a rightventricular tip electrode32, a rightventricular ring electrode34, a right ventricular (RV)coil electrode36, and anSVC coil electrode38. Typically, theright ventricular lead30 is transvenously inserted into theheart12 so as to place the rightventricular tip electrode32 in the right ventricular apex so that the RV coil electrode will be positioned in the right ventricle and theSVC coil electrode38 will be positioned in the superior vena cava. Accordingly, theright ventricular lead30 is capable of receiving cardiac signals, and delivering stimulation in the form of pacing and shock therapy to the right ventricle.

Thestimulation device10 is further connected to a His Bundle lead21 having a Histip electrode16, such as a helical active fixation device and a Hisring electrode19 located approximately 12 mm proximal from the Histip electrode16. The His Bundle lead21 is transvenously inserted into theheart12 so that the Histip electrode16 may be positioned in the tissue of the His Bundle. Accordingly, the His Bundle lead21 is capable of receiving depolarization signals propagated in the His Bundle or delivering stimulation to the His Bundle, creating a depolarization that can be propagated through the lower conductive pathways of the right and left ventricles (i.e., the right and left bundle branches and Purkinje fibers).

The His Bundle lead21 will be described in greater detail in conjunction with FIGS. 4 and 5.

An alternative embodiment of the present invention is shown in FIG. 2 in which a dualchamber stimulation device210 is in communication with one atrium, one ventricle, and the His Bundle. Though not explicitly illustrated in FIG. 2, a right atrial lead20 (shown in FIG. 1) can be optionally included. Thestimulation device210 maintains communication with the right atrium of theheart12 via a rightatrial lead20 having at least an atrial tip electrode22 and anatrial ring electrode23, that is implanted in the patient's right atrial appendage as described earlier in connection with FIG. 1, and aSVC coil electrode239.

A His Bundle (or His)lead221, having a Histip electrode216 and a Hisring electrode219, is positioned such that the Histip electrode216 is proximate the His Bundle tissue. Thestimulation device210 is also shown in FIG. 2 to be in electrical communication with the patient'sheart12 by way of aright ventricular lead230 having, in this embodiment, a rightventricular tip electrode232, a rightventricular ring electrode234, and a rightventricular coil electrode236.

Referring now to FIG. 3, there is illustrated a simplified block diagram of the multi-chamberimplantable stimulation device10 of FIG. 1, which is capable of treating both fast and slow arrhythmias with stimulation therapy, including cardioversion, defibrillation, and pacing stimulation. While a particular multi-chamber device is shown, this is for illustration purposes only, and one of skill in the art could readily duplicate, eliminate or disable the appropriate circuitry in any desired combination to provide a device capable of treating the appropriate chamber(s) with cardioversion, defibrillation and pacing stimulation.

Thehousing40 for thestimulation device10, shown schematically in FIG. 3, is often referred to as the “can”, “case” or “case electrode” and may be programmably selected to act as the return electrode for all “unipolar” modes. Thehousing40 may further be used as a return electrode alone or in combination with one or more of the coil electrodes,28,36 and38 (FIG.1), for shocking purposes. Thehousing40 further includes a connector (not shown) having a plurality of terminals,42,44,46,48,52,54,56,58,50, and51 (shown schematically and, for convenience, the names of the electrodes to which they are connected are shown next to the terminals). As such, to achieve right atrial sensing and pacing, the connector includes at least a right atrial tip terminal (A_RTIP)42 adapted for connection to the atrial tip electrode22 (FIG.1).

To achieve left chamber sensing, pacing and shocking, the connector includes at least a left ventricular tip terminal (V_LTIP)44, a left atrial ring terminal (A_LRING)46, and a left atrial shocking terminal (A_LCOIL)48, which are adapted for connection to the leftventricular ring electrode26, the leftatrial tip electrode27, and the leftatrial coil electrode28, respectively (FIG.1).

To support right chamber sensing, pacing and shocking, the connector further includes a right ventricular tip terminal (V_RTIP)52, a right ventricular ring terminal (V_RRING)54, a right ventricular shocking terminal (R_VCOIL)56, and an SVC shocking terminal (SVC COIL)58, which are adapted for connection to the rightventricular tip electrode32, rightventricular ring electrode34, theRV coil electrode36, and theSVC coil electrode38, respectively (FIG.1).

To achieve His Bundle sensing, or sensing and stimulation, the connector further includes a His Bundlelead tip terminal50 and a His Bundlelead ring terminal51 which are adapted for connection to the Histip electrode16 and the Hisring electrode19, respectively (FIG.1).

At the core of thestimulation device10 is aprogrammable microcontroller60 which controls the various modes of stimulation therapy. As is well known in the art, themicrocontroller60 typically includes a microprocessor, or equivalent control circuitry, designed specifically for controlling the delivery of stimulation therapy and may further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. Typically, themicrocontroller60 includes the ability to process or monitor input signals (data) as controlled by a program code stored in a designated block of memory. The details of the design and operation of themicrocontroller60 are not critical to the present invention. Rather, anysuitable microcontroller60 may be used that carries out the functions described herein. The use of microprocessor-based control circuits for performing timing and data analysis functions are well known in the art.

As shown in FIG. 3, anatrial pulse generator70 and aventricular pulse generator72 generate pacing stimulation pulses for delivery by the rightatrial lead20, theright ventricular lead30, thecoronary sinus lead24, and/or the His Bundle lead21 via anelectrode configuration switch74. It is understood that in order to provide stimulation therapy in each of the four chambers of the heart, the atrial and ventricular pulse generators,70 and72, may include dedicated, independent pulse generators, multiplexed pulse generators, or shared pulse generators. The pulse generators,70 and72, are controlled by themicrocontroller60 via appropriate control signals,76 and78, respectively, to trigger or inhibit the stimulation pulses. As used herein, the shape of the stimulation pulses is not limited to an exact square or rectangular shape, but may assume any one of a plurality of shapes which is adequate for the delivery of an energy pulse, packet, or stimulus.

Themicrocontroller60 further includestiming control circuitry79 which is used to control the timing of such stimulation pulses (e.g., pacing rate) as well as to keep track of the timing of refractory periods, blanking intervals, noise detection windows, evoked response windows, alert intervals, marker channel timing, etc., which is well known in the art.

According to one embodiment of the present invention,timing control circuitry79 also controls the onset and duration of a His signal sensing window during which a depolarization signal conducted through the atrioventricular node to the His Bundle can be detected.Timing control circuitry79 also controls a timing delay provided after a detected His signal detection, prior to the delivery of a right and/or left ventricular stimulation pulse.

Theswitch74 includes a plurality of switches for connecting the desired electrodes to the appropriate I/O circuits, thereby providing complete electrode programmability. Accordingly, theswitch74, in response to acontrol signal80 from themicrocontroller60, determines the polarity of the stimulation pulses (e.g., unipolar, bipolar, cross-chamber, etc.) by selectively closing the appropriate combination of switches (not shown) as is known in the art.

Atrial sensing circuits82 andventricular sensing circuits84 may also be selectively coupled to the rightatrial lead20,coronary sinus lead24, and theright ventricular lead30, through theswitch74 for detecting the presence of cardiac activity in each of the four chambers of the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR. SENSE) sensing circuits,82 and84, may include dedicated sense amplifiers, multiplexed amplifiers, or shared amplifiers. Theswitch74 determines the “sensing polarity” of the cardiac signal by selectively closing the appropriate switches, as is also known in the art. In this way, the clinician may program the sensing polarity independent of the stimulation polarity.

According to one embodiment of the present invention, a Hissensing circuit83 is selectively coupled to the His Bundle lead21 for detecting the presence of a conducted depolarization arising in the atria and conducted to the bundle of His via the atrioventricular node. As used herein, each of theatrial sensing circuit82, theventricular sensing circuit84, and the Hissensing circuit83, includes a discriminator, which is a circuit that senses and can indicate or discriminate the origin of a cardiac signal in each of the cardiac chambers.

Each sensing circuit,82,83 and84, preferably employs one or more low power, precision amplifiers with programmable gain and/or automatic gain control, bandpass filtering, and a threshold detection circuit, as known in the art, to selectively sense the cardiac signal of interest. The automatic gain control enables thedevice10 to deal effectively with the difficult problem of sensing the low amplitude signal characteristics of atrial or ventricular fibrillation.

The outputs of the atrial, His, and ventricular sensing circuits,82,83 and84, respectively, are connected to themicrocontroller60 which, in turn, is able to trigger or inhibit the atrial and ventricular pulse generators,70 and72, respectively, in a demand fashion in response to the absence or presence of cardiac activity in the appropriate chambers of the heart.

The sensing circuits,82,83, and84, in turn, receive control signals over signal lines,86 and88, from themicrocontroller60 for purposes of controlling the gain, threshold, polarization charge removal circuitry (not shown), and the timing of any blocking circuitry (not shown) coupled to the inputs of thesensing circuits82 and86.

For arrhythmia detection, thestimulation device10 includes anarrhythmia detector77 that utilizes the atrial and ventricular sensing circuits,82 and84, to sense cardiac signals to determine whether a rhythm is physiologic or pathologic. As used herein “sensing” is reserved for the noting of an electrical signal, and “detection” is the processing of these sensed signals and noting the presence of an arrhythmia. The timing intervals between sensed events (e.g., P-waves, R-waves, and depolarization signals associated with fibrillation) are then classified by themicrocontroller60 by comparing them to a predefined rate zone limit (i.e., bradycardia, normal, low rate VT, high rate VT, and fibrillation rate zones) and various other characteristics (e.g., sudden onset, stability, physiologic sensors, and morphology, etc.) in order to determine the type of remedial therapy that is needed (e.g., bradycardia pacing, anti-tachycardia pacing, cardioversion shocks or defibrillation shocks, collectively referred to as “tiered therapy”).

Cardiac signals are also applied to the inputs of an analog-to-digital (A/D)data acquisition system90 represented by an A/D converter. Thedata acquisition system90 is configured to acquire intracardiac electrogram signals, convert the raw analog data into a digital signal, and store the digital signals for later processing and/or telemetric transmission to anexternal device102. Thedata acquisition system90 is coupled to the rightatrial lead20, theHis Bundle lead21, thecoronary sinus lead24, and theright ventricular lead30 through theswitch74 to sample cardiac signals across any pair of desired electrodes.

In a preferred embodiment, thedata acquisition system90 is coupled tomicrocontroller60, or to other detection circuitry, for detecting a desired feature of the His Bundle signal. In one embodiment, anaverager65 is used to determine a sliding average of the His Bundle signal during a His signal sensing window using known or available signal averaging techniques.

Advantageously, thedata acquisition system90 may be coupled to the microcontroller, or other detection circuitry, for detecting an evoked response from theheart12 in response to an applied stimulus, thereby aiding in the detection of “capture”. Capture occurs when an electrical stimulus applied to the heart is of sufficient energy to depolarize the cardiac tissue, thereby causing the heart muscle to contract. Themicrocontroller60 detects a depolarization signal during a window following a stimulation pulse, the presence of which indicates that capture has occurred. Themicrocontroller60 enables capture detection by triggering theventricular pulse generator72 to generate a stimulation pulse, starting a capture detection window using thetiming control circuitry79 within themicrocontroller60, and enabling thedata acquisition system90 viacontrol signal92 to sample the cardiac signal that falls in the capture detection window and, based on the amplitude, determines if capture has occurred.

Capture detection may occur on a beat-by-beat basis or on a sampled basis. Preferably, a capture threshold search is performed at least once a day during at least the acute phase (e.g., the first 30 days) and less frequently thereafter. A capture threshold search would begin at a desired starting point (either a high energy level or the level at which capture is currently occurring) and decrease the energy level until capture is lost. The value at which capture is lost is known as the capture threshold. Thereafter, a safety margin can be automatically or programmably added to the capture threshold.

Themicrocontroller60 is further coupled to amemory94 by a suitable data/address bus96, wherein the programmable operating parameters used by themicrocontroller60 are stored and modified, as required, in order to customize the operation of thestimulation device10 to suit the needs of a particular patient. Such operating parameters define, for example, pacing pulse amplitude, pulse duration, electrode polarity, rate, sensitivity, automatic features, arrhythmia detection criteria, and the amplitude, waveshape and vector of each shocking pulse to be delivered to the patient'sheart12 within each respective tier of therapy.

Advantageously, the operating parameters of theimplantable device10 may be non-invasively programmed into thememory94 through atelemetry circuit100 in telemetric communication with theexternal device102, such as a programmer, transtelephonic transceiver, or a diagnostic system analyzer. Thetelemetry circuit100 is activated by the microcontroller by acontrol signal106. Thetelemetry circuit100 advantageously allows intracardiac electrograms and status information relating to the operation of the device10 (as contained in themicrocontroller60 or memory94) to be sent to theexternal device102 through an establishedcommunication link104.

In the preferred embodiment, thestimulation device10 further includes aphysiologic sensor108, commonly referred to as a “rate-responsive” sensor because it is typically used to adjust pacing stimulation rate according to the exercise state of the patient. However, thephysiological sensor108 may further be used to detect changes in cardiac output, changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states). Accordingly, themicrocontroller60 responds by adjusting the various pacing parameters (such as rate, stimulation delays, etc.) at which the atrial and ventricular pulse generators,70 and72, generate stimulation pulses.

A common type of rate responsive sensor is an activity sensor, such as an accelerometer or a piezoelectric crystal, which is mounted within thehousing40 of thestimulation device10. Other types of physiologic sensors are also known, for example, sensors which sense the oxygen content of blood, respiration rate and/or minute ventilation, pH of blood, ventricular gradient, etc. However, any suitable sensor may be used which is capable of sensing a physiological parameter which corresponds to the exercise state of the patient. The type of sensor used is not critical to the present invention and is shown only for completeness.

The stimulation device additionally includes abattery110 which provides operating power to all of the circuits shown in FIG.3. For thestimulation device10, which employs shocking therapy, thebattery110 must be capable of operating at low current drains for long periods of time, and then be capable of providing high-current pulses (for capacitor charging) when the patient requires a shock pulse. Thebattery110 must also have a predictable discharge characteristic so that elective replacement time can be detected. Accordingly, thedevice10 preferably employs lithium/silver vanadium oxide batteries, as is true for most (if not all) current devices.

Thedevice10 is shown in FIG. 3 as having animpedance measuring circuit112 which is enabled by themicrocontroller60 via acontrol signal114. The known uses for animpedance measuring circuit112 include, but are not limited to, lead impedance surveillance during the acute and chronic phases for detecting proper lead positioning or dislodgement; detecting operable electrodes and conductors; and automatically switching to an operable pair if dislodgement or electrical disruption occurs; measuring respiration or minute ventilation; measuring thoracic impedance for determining shock thresholds; detecting when the device has been implanted; measuring stroke volume; and detecting the opening of heart valves, etc. Theimpedance measuring circuit112 is advantageously coupled to theswitch74 so that any desired electrode may be used.

According to one embodiment of the present invention, the Histip electrode16 and Hisring electrode19 may be selectively coupled viaswitch74 to theimpedance measuring circuit112 for performing a tissue impedance measurement. The tissue impedance measurement is made to determine the location of the His Bundle as the Histip electrode16 ormapping collar418 as shown in FIG. 4, or sensing electrodes420,421,422,423 as shown in FIG. 5, is advanced along the endocardial surface of the right atrium. A method for performing this tissue impedance measurement using the His Bundle lead21 will be described further in conjunction with FIG.6.

In the case where thestimulation device10 is intended to operate as an implantable cardioverter/defibrillator (ICD) device, it must detect the occurrence of an arrhythmia, and automatically apply an appropriate electrical shock therapy to the heart aimed at terminating the detected arrhythmia. To this end, themicrocontroller60 further controls ashocking circuit116 by way of acontrol signal118. Theshocking circuit116 generates shocking pulses of low (up to 0.5 joules), moderate (0.5-10 joules), or high energy (11 to 40 joules), as controlled by themicrocontroller60. Such shocking pulses are applied to the patient'sheart12 through at least two shocking electrodes, and as shown in this embodiment, selected from the leftatrial coil electrode28, theRV coil electrode36, and/or theSVC coil electrode38. As noted above, thehousing40 may act as an active electrode in combination with theRV electrode36, or as part of a split electrical vector using theSVC coil electrode38 or the left atrial coil electrode28 (i.e., using the RV electrode as a common electrode).

Cardioversion shocks are generally considered to be of low to moderate energy level (so as to minimize pain felt by the patient), and/or synchronized with an R-wave and/or pertaining to the treatment of tachycardia. Defibrillation shocks are generally of moderate to high energy level (i.e., corresponding to thresholds in the range of 5-40 joules), delivered asychronously (since R-waves may be too disorganized), and pertaining exclusively to the treatment of fibrillation. Accordingly, themicrocontroller60 is capable of controlling the synchronous or asynchronous delivery of the shocking pulses.

A more detailed illustration of the His Bundle lead21 is shown in FIG.4. At the distal end of thelead21 is the HisBundle tip electrode16. The HisBundle tip electrode16 is, or includes, an active fixation device, preferably a helical, “screw-in,” device that allows stable fixation of the electrode in the His Bundle tissue.

The distal end of the His Bundle lead21 is further provided with a non-traumatic conductive surface (also referred to herein interchangeably as mapping collar)418. The non-traumaticconductive surface418 is advantageously used to make electrical measurements that indicate the location of the His Bundle without having to anchor the HisBundle tip electrode16 into the endocardial tissue. The non-traumaticconductive surface418 and the HisBundle tip electrode16 are electrically coupled within the lead body of theHis Bundle lead21 and together form one conductive element for the purposes of sensing, stimulation, and impedance measurements. Drugs, for example an acute anti-arrhythmic drug such as lidocaine and/or an anti-inflammatory agent such as dexamethazone sodium phosphate, can be stored, for example, within a reservoir (not shown) at the base of the HisBundle tip electrode16 for local dispensation.

The His Bundle lead21 is also provided with a Hisring electrode19. The Hisring electrode19 is preferably spaced between approximately 2 mm and 30 mm, but preferably 10 mm, from the Histip electrode16. The Hisring electrode19 may function as the return electrode during bipolar sensing, stimulation or impedance measurement operations.

The Histip electrode16 and the Hisring electrode19 are each connected toflexible conductors64 and66, respectively, running the entire length of theHis Bundle lead21. Theflexible conductor64 is connected to the Histip electrode16 and is electrically insulated from theflexible conductor66 by a layer of insulation. Theconductor66 is connected to the Hisring electrode19. Theflexible conductors64 and66 serve to electrically couple the Hisring electrode19 and the Histip electrode16 to the Hisring electrode terminal51 and the Histip electrode terminal50, respectively. One embodiment of the His Bundle lead21 is available from St. Jude Medical CRMD as lead model No. 1488T.

FIG. 5 illustrates an In an alternative Hislead31 that is generally similar in function and design to the Hislead21. The Hislead31 is provided with a Histip electrode16 that includes multiple, round, closely-spacedconductive surfaces520,521,522,523 that are arranged on a distalmost face518 of thelead31, directly facing the His Bundle tissue. Though four roundconductive surfaces520,521,522,523 are shown herein as being uniformly distributed around the Histip electrode16 and are electrically separated from each other by insulating material, it should be clear that a different number of conductive surfaces may alternatively be selected.

In one embodiment, a conductive surface, e.g.520 is connected to its own flexible conductor, e.g.564 that extends along the length of theHis Bundle lead31. The remainingconductive surfaces521,522,523 are electrically connected together and are also connected to aflexible conductor566 that extends along the length of theHis Bundle lead31. The flexible conductors, e.g.526,527 are insulated from each other.

In this embodiment, thedevice10 includes two separate connection terminals, one for each of the twoflexible conductors564,566, that are further connected to switch74. The twoflexible conductors564,566 can then be selectively connected as desired to the Hissensing circuit83,ventricular pulse generator72, orimpedance measuring circuit112 for sensing, stimulating, and measuring tissue impedance at the site of the His Bundle (FIG.3).

Using thelead31, it is possible to effect stimulation with the Histip electrode16 and the Hisring electrode19, and to effect sensing with theconductive surfaces520,521,522,523. According to another design, the sensing is effected by theconductive surfaces520,521,522,523 and stimulation is effected by means of the leads other than the Hislead31, for example the rightatrial lead20. For more details regarding a heart electrode equipped with multiple conductive surfaces, reference is made to U.S. Pat. Nos. 5,306,292 and 5,645,580, which are incorporated herein by reference.

During the implantation procedure, the His Bundle lead21 of FIG. 4 (or the His Bundle lead31 of FIG. 5) is introduced transvenously into the right atrium. It is then gradually advanced with the Histip electrode16 in contact with the endocardial tissue. Electrical measurements are made continuously as the Histip electrode16 is advanced to determine the location of the His Bundle. The non-traumaticconductive surface418 advantageously provides electrical contact with the endocardial tissue thereby allowing electrical measurements to be performed without having to fix the Histip electrode16 into the endocardial tissue using the HisBundle tip electrode16.

In a preferred embodiment, tissue impedance measurements are made in order to locate the His Bundle. The equivalent circuit diagram depicted in FIG. 6 represents a model by which a tissue impedance measurement can be made using the His Bundle lead21 of FIG.4. An excitation current is applied through the Histip electrode16. The excitation current is preferably provided as a current limited high-frequency alternating current signal produced by a30kHz oscillator550 passing through acurrent limiter552. A voltage signal can then be measured between the His tip electrode16 (or the non-traumatic conductive surface418) and the Hisring electrode19 in a bipolar fashion. The voltage signal is related to the supplied current and thetissue impedance554 associated with the tissue in contact with the Histip electrode16. Thus, the measured voltage signal is processed by theimpedance measuring circuit112 to determine the impedance of the tissue in contact with Histip electrode16. The impedance equals the voltage divided by the current.

Right atrial tissue impedance is expected to be approximately twice that of the His Bundle. Using the foregoing measurement method, the right atrial tissue impedance is typically on the order of 1200 to 1500 ohms, whereas the His Bundle tissue impedance is typically on the order of 600 to 800 ohms. Other impedance values can be obtained using different measurement techniques. Thus, as the His Bundle lead21 is advanced in the right atrium, a large decrease in measuredtissue impedance554, of approximately 50%, indicates that the His Bundle tip electrode15 is proximate the His Bundle.

The HisBundle tip electrode16 may then be secured in the His Bundle thereby anchoring the Histip electrode16 in contact with the His Bundle tissue. The electrogram signal arising from the His Bundle can then be received by the Hissensing circuit83. Preferably, a bypass filter (not shown) that allows signals ranging between 30 Hz and 200 Hz to be received is used to block the high frequency alternating current excitation signal produced by theoscillator550.

FIG. 7 illustrates a flow chart of an operation implemented by thedevice stimulation10 according to the present invention. In this flow chart, and other flow charts presented herein, the various algorithmic steps are summarized in individual “blocks”. Such blocks describe specific actions or decisions that must be made or carried out as the algorithm proceeds. Where a microcontroller (or equivalent) is employed, the flow charts presented herein provide the basis for a “control program” that may be used by such a microcontroller (or equivalent) to effectuate the desired control of the stimulation device. Those skilled in the art may readily write such a control program based on the flow charts and other descriptions presented herein.

The algorithm of FIG. 7 represents amethod600 for triggering ventricular stimulation based on the detection of the His Bundle signal. Beginning atstep605,microcontroller60 determines the rate indicated by thephysiologic sensor108 that would meet the patient's current metabolic demand. Ifmethod600 determines atdecision step610 that the sensed atrial rate is lower than the metabolic need as indicated by thephysiological sensor108, an atrial stimulation pulse is delivered atstep615. The His signal sensing window is initiated after the atrial stimulation pulse atstep630. The onset and duration of the His signal sensing window following an atrial stimulation pulse are preferably programmable settings. If the intrinsic atrial rate adequately meets the physiologic sensor indicated rate as determined atdecision step610, then a His signal sensing window is initiated atstep630 after detection of the next P-wave atstep625. The His signal sensing window should typically begin immediately upon detection of the P-wave, but the onset and duration of the His signal sensing window are preferably both programmable settings and may be the same or different than the His signal sensing window following an atrial stimulation pulse. The appropriate duration of the His signal sensing window may vary between patients and could range from approximately 50 ms to approximately 200 ms.

During the His signal sensing window, the His Bundle signal is sampled, as indicated atstep635, by Hissensing circuit83 at a predetermined sampling frequency that may range between approximately 50 Hz and 2 kHz. The sampled signal data is received bymicroprocessor60 to be averaged according to modern signal averaging methods byaverager65.

Preferably, a “sliding” average of the His Bundle signal is obtained atstep635. A “sliding” average is determined byaverager65 by averaging the sampled signal points over an averaging interval of, for example, approximately 0 to 150 ms. The sliding average is calculated on a “first-in-first-out” basis meaning that a new sampling point replaces the oldest sampling point in calculating the sliding average.

Whenmicroprocessor60 detects a peak in the sliding average of the His Bundle signal, as determined atdecision step640, a right ventricular stimulation pulse and/or a left ventricular pulse are triggered atstep650. The right and left ventricular stimulation pulses may be delivered almost immediately (preferably with some delay), or they may be delivered after a programmed delay following the detected His signal peak. The delay after the detected peak until right ventricular stimulation pulse delivery may be the same or different than the delay until left ventricular stimulation pulse delivery. The right and left ventricular stimulation pulses are generated byventricular pulse generator72 and delivered via the desired pair of electrodes usingright ventricular lead30 and/orcoronary sinus lead24, respectively.

Ifmicroprocessor60 does not detect a peak of sufficient amplitude and the His signal sensing window expires as determined atstep645, the right and left ventricular stimulation pulses are delivered upon expiration of the His signal sensing window atstep650. Otherwise, the His Bundle signal continues to be sampled and averaged atstep635 until a peak is detected or until the sensing window expires.

Thus, according tomethod600 illustrated in FIG. 7, ventricular stimulation pulses may be delivered to the right and left ventricles at an optimal time based on the conduction of an atrial depolarization through the atrioventricular node and His Bundle. It is expected that this natural conduction timing is most beneficial to the patient.

In an alternative embodiment, the His Bundle lead21 may be used for stimulating the ventricles at the site of the His Bundle as well as sensing the His Bundle signal. His Bundle stimulation may be beneficial to patients having intermittent or partial atrioventricular block but intact ventricular conduction pathways below the level of the atrioventricular node. When no His signal is detected due to a return of atrioventricular block, stimulation may be delivered to the His Bundle to depolarize the ventricles. A stimulation pulse delivered by the His Bundle lead21 that successfully depolarizes the His Bundle will cause the depolarization to be conducted throughout the ventricular chambers via the normal left and right bundle branches and Purkinje fibers.

In this embodiment, if the His signal sensing window expires atstep645, the ventricular stimulation pulse delivered atstep650 of FIG. 7 is delivered by theHis Bundle lead21. The stimulation pulse may be delivered in a unipolar fashion using the His Bundle tip electrode15 and thedevice housing40 or in a bipolar fashion using the HisBundle tip electrode16 and the HisBundle ring electrode19. The HisBundle tip electrode16 and the HisBundle ring electrode19 are connected according to the selected stimulation polarity viaswitch74 to theventricular pulse generator72.

It is recognized that the His Bundle signal may be analyzed in numerous ways such that characteristics other than a peak in the sliding average can be used to trigger the delivery of ventricular stimulation pulses. For example, the median or mode of the integrated voltage signal may be determined as the point in time upon which ventricular stimulation is based. The flow chart of FIG. 8 illustrates analternative method700 for analyzing the His Bundle signal and triggering ventricular stimulation.

Method700 of FIG. 8 begins in the same way as the method of FIG.7. The sensor-indicated rate is determined atstep705 and compared to the atrial rate atstep710. If the atrial rate is too low, an atrial stimulation pulse is delivered atstep715. If the atrial rate is not too low, the atrial P-wave is detected atstep720. Both an atrial stimulation pulse and a sensed atrial P-wave will cause the His signal sensing window to be initiated atstep725. Atstep730, the method of FIG. 8 samples and integrates the His signal over the entire duration of the His signal sensing window rather than determining a sliding average as in the method of FIG.7.

These events are also portrayed in the timing diagram shown in FIG.9. On the atrial channel, anatrial event305, either a sensed P-wave or an atrial stimulation pulse, is followed by a Hissignal sensing window310. The onset and the duration of the His signal sensing window are predefined, preferably programmable, values which may also depend on whether theatrial event305 was a stimulation pulse or a sensed P-wave. The Hissignal315 is integrated over the entire Hissignal sensing window310 to determine the area under the Hissignal315 shown as thesignal integral320. The point in time at which half of the area of the signal integral320 has been reached is then determined bymicroprocessor60 as the median325 of the Hissignal integral320.

Thus, atstep735 of FIG. 8, the temporal location of the median325 of the His signal integral320 is determined. Atstep740, a predefined delay is added to the time at which the median325 occurred. After the delay expires, ventricular stimulation is delivered atstep750. Ventricular stimulation may be delivered to one or, preferably, both ventricular chambers. Hence, thedelay330 precedingventricular stimulation335 shown in FIG. 9 may be a programmable setting with the delay to right ventricular stimulation and the delay to left ventricular stimulation being equal or each uniquely defined.

Thus, a method and apparatus has been provided which deliver ventricular stimulation at an optimal time after an atrial event according to the natural conduction rate of the atrioventricular node and His Bundle. In patients having intermittent of total atrioventricular block, a method and apparatus has been provided which allows stimulation of the His Bundle such that the ventricles are depolarized via the remaining natural conduction system. While the present invention has been described according to specific embodiments, this description is intended for illustration and not limitation. Those skilled in the art may modify features or methods described herein without departing from the scope of the present invention as set forth in the following claims. It will also be appreciated by a person of ordinary skill in the art that the delay should be sufficient to allow the integration of the signal for determining an accurate medium or mode.

Claims (45)

What is claimed is:

1. A cardiac stimulation device to deliver ventricular stimulation pulses following an atrial depolarization, comprising:

a His Bundle sense electrode disposed in proximity to a Bundle of His;

a stimulation electrode to deliver the ventricular stimulation pulses;

a sense circuit coupled to the His Bundle sense electrode to detect a conduction signal which is naturally conducted through an AV node into the Bundle of His;

a timing control circuit coupled to the His Bundle sense electrode and the sense circuit to initiate a His Bundle signal sensing window;

a sampler to sample the detected conduction signal during the His Bundle signal sensing window; and

a processor to deliver the ventricular stimulation pulses based on the detected conduction signal.

2. A cardiac stimulation device to deliver ventricular stimulation pulses following an atrial depolarization, comprising:

a plurality of electrodes including an atrial sense electrode for sensing the atrial depolarization, a His Bundle sense electrode disposed in proximity to a Bundle of His, and a stimulation electrode for delivering the ventricular stimulation pulses;

a sense circuit, coupled to the His Bundle sense electrode, that detects a conduction signal which is naturally conducted through an AV node into the Bundle of His;

a timing control circuitry connected to the His Bundle sense electrode and the sense circuit to initiate a His Bundle signal sensing window following the sensing of the atrial depolarization;

a sampler that samples the detected conduction signal during the His Bundle signal sensing window; and

a pulse generator, connected to the stimulation electrode, to deliver the ventricular stimulation based on a detected conduction signal.

3. The cardiac stimulation device ofclaim 2, wherein the His Bundle signal sensing window extends for approximately 200 ms.

4. The cardiac stimulation device ofclaim 3, wherein the pulse generator generates the ventricular stimulation pulses to a right ventricular chamber.

5. The cardiac stimulation device ofclaim 3, wherein the pulse generator generates the ventricular stimulation pulses to a left ventricular chamber.

6. The cardiac stimulation device ofclaim 3, wherein the pulse generator generates stimulation pulses for delivery to the Bundle of His.

7. The cardiac stimulation device ofclaim 3, wherein the pulse generator generates the ventricular stimulation pulses to at least one of a right ventricular chamber and a left ventricular chamber.

8. The cardiac stimulation device ofclaim 7, wherein the pulse generator generates a stimulation pulse directly to the Bundle of His to induce ventricular contraction.

9. The cardiac stimulation device ofclaim 7, wherein the timing control circuitry sets a first AV delay from the detected conduction signal to the delivery of the ventricular stimulation pulse to at least one of the right ventricular chamber and the left ventricular chamber.

10. The cardiac stimulation device ofclaim 9, further including an averager that determines a moving average of the conduction signal to determine a His signal peak; and

wherein the pulse generator generates the ventricular stimulation pulse following a detection of the His signal peak.

11. The cardiac stimulation device ofclaim 9, further including an integrator that determines a median of the conduction signal; and

wherein the pulse generator generates the ventricular stimulation pulse following a detection of the median.

12. The cardiac stimulation device ofclaim 2, further including a His Bundle tip electrode secured to the Bundle of His to deliver a stimulation pulse to the Bundle of His.

13. The cardiac stimulation device ofclaim 12, wherein the His Bundle sense electrode includes a plurality of sense electrodes that are spaced apart in proximity to the His Bundle tip electrode, and that are disposed in contact with the Bundle of His.

14. The cardiac stimulation device ofclaim 12, further including a mapping collar that is disposed in proximity and is electrically coupled to the His Bundle tip electrode.

15. The cardiac stimulation device ofclaim 14, wherein the His Bundle sense electrode includes a His Bundle ring electrode that is distally located relative to the mapping collar.

16. The cardiac stimulation device ofclaim 14 further including a reservoir disposed in proximity to the mapping collar, for storing a medicament.

17. A cardiac stimulation device to deliver ventricular stimulation pulses following an atrial stimulation pulse, comprising:

a plurality of electrodes including an atrial stimulation electrode for delivering the atrial stimulation pulse, a His Bundle sense electrode disposed in proximity to a Bundle of His, and a ventricular stimulation electrode for delivering the ventricular stimulation pulses;

a sense circuit, coupled to the His Bundle sense electrode, that detects a conduction signal which is naturally conducted through an AV node into the Bundle of His;

a timing and control circuit connected to the His Bundle sense electrode and the sense circuit to initiate a His Bundle signal sensing window following a sensing of the atrial stimulation pulse;

a sampler that samples the detected conduction signal during the His Bundle signal sensing window; and

a pulse generator, connected to the ventricular stimulation electrode, to deliver the ventricular stimulation pulses based on the defected conduction signal.

18. The cardiac stimulation device ofclaim 17, wherein the timing control circuitry sets a first AV delay from the detected conduction signal to the delivery of the ventricular stimulation pulse to at least one of a right ventricular chamber and a left ventricular chamber.

19. The cardiac stimulation device ofclaim 17, wherein the pulse generator generates stimulation pulses for delivery to the Bundle of His.

20. A cardiac stimulation device for delivering ventricular stimulation pulses following an atrial depolarization, comprising:

an atrial sensing means for sensing the atrial depolarization;

a His Bundle sensing means disposed in proximity to a Bundle of His;

a stimulation means for delivering the ventricular stimulation pulses;

means for detecting a conduction signal which is naturally conducted through an AV node into the Bundle of His;

a sampler to sample the detected conduction signal; and

means for delivering the:ventricular stimulation pulses based on the detected conduction signal.

21. The cardiac stimulation device ofclaim 20, further including a means for initiating a His Bundle signal sensing window following the sensing of the atrial depolarization.

22. The cardiac stimulation device ofclaim 21, wherein the initiating means sets a first AV delay from the detected conduction signal to the delivery of the ventricular stimulation pulse to at least one of the right ventricular chamber and the left ventricular chamber.

23. A cardiac stimulation device for delivering ventricular stimulation pulses following an atrial stimulation pulse, comprising:

a His Bundle sensing means disposed in proximity to a Bundle of His;

a stimulation means for delivering the ventricular stimulation pulses and the atrial stimulation pulse;

means for detecting a conduction signal which is naturally conducted through an AV node into the Bundle of His;

a sampler to sample the detected conduction signal; and

means for delivering the ventricular stimulation pulses based on a delivered atrial stimulation pulse.

24. The cardiac stimulation device ofclaim 23, further including means for initiating a His Bundle signal sensing window following the delivery of the atrial stimulation pulse; and

wherein the initiating means sets a first AV delay from the detected conduction signal to the delivery of the ventricular stimulation pulse to at least one of the right ventricular chamber and the left ventricular chamber.

25. A method of delivering ventricular stimulation pulses following an atrial depolarization comprising:

initiating a I-Us Bundle signal sensing window;

detecting a conduction signal that is naturally conducted through an AV node into a Bundle of His;

sampling the detected conduction signal during the His Bundle signal sensing window; and

delivering the ventricular stimulation pulses based on the detected conduction signal.

26. A method of delivering ventricular stimulation pulses following an atrial depolarization, comprising the steps of:

sensing the atrial depolarization;

initiating is Bundle signal sensing window following the sensing of the atrial depolarization;

detecting a conduction signal that is naturally conducted through an AV node into a Bundle of His;

sampling the detected conduction signal during the His Bundle signal sensing window; and

delivering a ventricular stimulation pulse based on the detected conduction signal.

27. A The method ofclaim 26, wherein the step of initiating the His Bundle signal sensing window includes extending the His Bundle signal sensing window for a predetermined length of time.

28. The method ofclaim 27, wherein the step of extending the His Bundle signal sensing window for a predetermined length of time includes extending the His Bundle signal sensing window for approximately 200 ms.

29. The method ofclaim 26, wherein the step of delivering the ventricular stimulation pulse includes stimulating a right ventricular chamber.

30. The method ofclaim 26, wherein the step of delivering the ventricular stimulation pulse includes stimulating a left ventricular chamber.

31. The method ofclaim 26, wherein the step of delivering the ventricular stimulation pulse includes stimulating a right ventricular chamber and a left ventricular chamber.

32. The method ofclaim 31, further including setting a first AV delay from the detected conduction signal to the delivery of the ventricular stimulation pulse to the right ventricular chamber.

33. The method ofclaim 31, further including setting a second AV delay from the method conduction signal to the delivery of the ventricular stimulation pulse to the left ventricular chamber, to achieve synchronization between left and right ventricular contractions.

34. The method ofclaim 31, wherein if the conduction signal is not detected, delivering a stimulation pulse directly to the Bundle of His to induce ventricular contraction.

35. The method ofclaim 26, wherein sampling the detected conduction signal during the His Bundle signal sensing window includes calculating a moving average of the conduction signal to determine a His signal peak.

36. The method ofclaim 35, further including the step of delivering the ventricular stimulation pulse following a detection of the His signal peak.

37. The method ofclaim 26, wherein sampling the detected conduction signal during the His Bundle signal sensing window includes calculating a median of the conduction signal.

38. The method ofclaim 37, further including the step of delivering the ventricular stimulation pulse following a detection of the median.

39. A method of delivering ventricular stimulation pulse following an atrial stimulation, comprising the steps of:

delivering the atrial stimulation;

initiating a His Bundle signal sensing window following the delivery of the atrial stimulation;

detecting a conduction signal that is naturally conducted through an AV node into a Bundle of His;

sampling the detected conduction signal during the His Bundle signal sensing window; and

delivering a ventricular stimulation pulse based on the detected conduction signal.

40. The method ofclaim 39, wherein the step of initiating the His Bundle signal sensing window includes extending the His Bundle signal sensing window for a predetermined length of time.

41. The method ofclaim 39, wherein the step of delivering the ventricular stimulation pulse includes stimulating at least one of a right ventricular chamber and a left ventricular chamber.

42. The method ofclaim 41, further including setting a first AV delay from the detected conduction signal to the delivery of the ventricular stimulation pulse to the right ventricular chamber; and

setting a second AV delay from the detected conduction signal to the delivery of the ventricular stimulation pulse to the left ventricular chamber, to achieve synchronization between left and right ventricular contractions.

43. The method ofclaim 39, wherein if the conduction signal is not detected, delivering a stimulation pulse directly to the Bundle of His to induce ventricular contraction.

44. The method ofclaim 39, wherein sampling the detected conduction signal during the His Bundle signal sensing window includes calculating a moving average of the conduction signal to determine a His signal peak; and

delivering the ventricular stimulation pulse following a detection of the signal peak.

45. The method ofclaim 39, wherein sampling the detected conduction signal during the His Bundle signal sensing window includes calculating a median of the conduction singal; and

delivering the ventricular stimulation pulse following a detection of the median.

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